1. Field of the Invention
This invention relates to replaceable machine parts that are exposed to high wear and repeated shock loading, such as teeth used on dragline buckets. Specifically, the system of this invention comprises using controlled tolerances at key attachment points to provide enhanced service life.
2. Description of the Prior Art
Digging and levelling apparatus such as draglines, backhoes, front-end loaders and like often use replaceable tooth assemblies which are mounted on the tooth horns to provide sacrificial parts that are exposed to the repeated shock loading and high wear occasioned by the digging operation. In prior art systems, each tooth assembly is characterized by a wedge-shaped adapter which mounts directly on the tooth horn of the bucket, shovel or alternative digging or scraping mechanism of the equipment. A wedge-shaped tooth point is frontally seated on and rigidly pinned to the adapter for engaging the material to be excavated.
Such prior art systems are characterized by rigid attachment of the tooth or wear part to the supporting adapter, with little or no play for movement of the tooth relative to the adapter and the supporting part of the equipment. As a result, the replaceable part is repeatedly exposed to the full impact of the shock loading that occurs during the digging operation (in the case of excavating equipment) or during normal operation of the machinery, as in the case of other types of machinery.
The prior art does not suggests that the life of replaceable teeth or other sacrificial parts exposed to repeated shock loading can be extended by providing specific ranges of tolerances that permit a loose fit between the sacrificial part and its supporting assembly. Indeed, heretofore a rigid fit has been regarded as essential. U.S. Pat. No. 5,435,084 (Immel), for example, teaches that any "play" between parts leads to increased wear and should be avoided.